Free scaling and free machining steel



Jn. 2, 1934- H..J. FRENCH ErAL 1,941,547

FREE SCALING AND FREE MCHINING STEEL Filed D'eo.I 22 1930 Patented Jan. 2, i934 STATES PATENT .OFFICE FREE SCALING AND FREE MACHINING l STEEL Wale Application December 22, 1930 Serial 4 claims.

The present invention relates to free scalingA and free machining alloy steels and, more particularly, to low alloy structural steels having free scaling and free machining properties.

It has been well known that improved lmechanical properties have been imparted to iron and steels by the incorporation of alloying elements therein, or by the heat treatment thereof, or by a combination of alloying and heat treatment.

When improved mechanical properties, such as high strength, or high resistance to fatigue, combined with toughness, or a high resistance to shock, were imparted to steels, for example, the latter became dimcult to fabricate due to an appreciable l in the ease of machining (i. e., turning, boring, reaming, milling, drilling, threading, and the like) and in the case of cold forming operations such as drawing, spinning and the like.A

Attempts were made to overcome these shortcomings in the ease of fabrication by incorporating in the steel various substances which were intended to improve the sc-called free cutting properties and the like. For instance, high sulphur with increased manganese or high sulphur with increased manganese and high phosphorus have been employed to improve the free cutting and free machining properties of steels. The addition of the foregoing substance or substances impaired or detrimentally aiected the mechanical properties of the steels. .Moreover, steels containing the foregoing substances were substantially like carbon steels or were only minor departures therefrom. A typical unalloyed (carbon) steel of the foregoing type is one containing about 0.08% to 0.16% C, about 0.60% to 0.80% Mn, about 0.09% to 0.13% P and about 0.075% to 0.15% S. Another illustration is a steel containing about 0.2% Cy. about 1.4% Mn, about 0.019% P, about 0.14% S and about .01 Si. Steels of the foregoing types do not have mechanical properties comparable to those of high grade alloy steels. For instance, the presence of high phosphorous, or high sulphur, or a combination of both causes a loss of ductility in these steels as well as a loss oi toughness. The phosphorous steels are cold short" and can oniy be subjected to a. limited 1.11m. of fabri eating operations.`

Although some proposals have been made to provide the art with free scaling and free machining alloyV steels having acceptable mechanical properties, none, as 'far as we are aware, has been suggested, which is practical and satisfactory in commercial and industrial use.

It is an object of the present invention to reinedy the foregoing shortcomings and to provide the art with free scaling and free machining alloy steels having unimpaired mechanical properties.

It is a further object of the invention to provide free scaling and free machining alloy steels in which greater use can be made of alloyingele- 00 ments or of heat treatment or of a-combination of the two to produce improved mechanical properties in'such alloy steels without the usual and customary relatively large decrease in the ease of machining or cold forming and the impairment 05 of free scaling properties.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction With the accompanying drawing in which:

Fig. 1 illustrates a 'diagrammatic view in a somewhat exaggerated manner of a photomicrograph of a cross section of a piece of steel embodying the present invention and showing the scale on the surface thereof; and

Fig. 2 is a view similar to Fig. 1 of a piece of ordinary or untreated nickel steel.

It has been discovered that when an appreciable amount of a metallic sulphide of the type of zirconium sulphide is introduced into low alloy, structural steels containing not more than about-'1% of alloyingelements, the treated steel has the property of free scaling and of nfree machining without having its mechanical properties such as, hardness, toughness and the like, adversely affected to any material or appreciable extent. It has been found that zirconium sulphide, for instance, is distributed throughout the steel in very minute particles and often in practically a submicroscopic state and that the scale on the improved steels has a unique constitution in that a porous friable layer or stratum of scale forms an intermediate or junctural layer between the body of the steel and the outer layers oi scale. This scale is more easily detached from the steel and decreases the Wear on cutting and forming tools, Which tools remain in a good condition and continue to produce a finely nished, accurate surface for a longer period of time than would be the case with the ordinary steels. Then again, the condition and distribution of the sulphide ci zirconium, for example, in the improved alloy steel is such that the power required in cutting the steel is lower than ordinarily coned and the smoothness and accuracy oi the 100 cut surfaces are improved and the rate of wear of the cutting tools is reduced. By the use of y the present improved steels, smoother and more accurate surfaces can beproduced with substau-fV tial economy over prior products. il@

The following specific examples of the invention are given for illustrative purposes and for a better understanding by those skilled in the art.

Example No. 1

In carrying the present invention into practice, a melt of steel composed of about 0.15% of carbon, 31/2% of nickel and the balance comprising iron plus the customary small amounts of Mn, Si, P, S, etc. is held in a suitable vessel such as a crucible, ladle, furnace or the like and 0.40% of zirconium sulphide, for example, is added to the melt and is given ample opportunity to distribute itself throughout the mass of molten metal or is caused to be distributed throughout said mass. This zirconium sulphide addition may be made as zirconium sulphide or as separate additions of the proper proportions of appropriate zirconium and sulphur containing materials. In the latter case, zirconium sulphide will be formed within the melt or molten metal.

When the zirconium sulphide is completely incorporated in the mass of metal, it is poured into molds or the like in a well known manner. As cast, rolled, pressed, forged, or otherwise fabricated into shape, it has been found that the new steel (hereafter termed untreated steel) has improvements over steel not treated as described herein. The following table shows a Vcomparison between the various physical properties of an ordinary untreated steel and a steel produced in accordance with the principles of the present invention as exemplified in the foregoing'procedure.-

Table Pro orties Untreated (ou quencne) from 1,475 F.) Treated Steel steel Proportional limit 25, 000 #/sq. in. Elongation in 2 inches 24. 0% 13. 5% Reduction o! area 46. 0% 40. 0% Izod impact, energy absorbed it. lbs 51 it. lbs.

In natural condition Treated steel Unstted Power to turn with same tool, at 56 it. per minute cutting speed 0.020 inch/rev. feed and l/l6 inch depth of cut 450 watts 810 watts Amount of scale roduced in 6 heatin s to l800 for )i hr. with lig t hammer tapping during cooling. Wgt. lost in milligrams from specimens l inch diameter by 2 inches long 4570 mgs. 2250 ings.

A steel embodying the present invention when examined under the microscopeL has a different structure than an ordinary steel. The differences may be clearly observed in photomicro.-

graphs of untreated and treated steels.

In Fig. 1 of the drawing, the reference character B designates the base, core or foundation of a piece of the improved alloy steel. The surface of the piece of steel is covered with scale S. This scale is dierent from ordinary scale and becomes loosened and disengaged from the foundation metal very easily. In fact, it has been found that the new steel possesses a unique and distinct free scaling character. For example, tests show that more than about double the amount of scale will drop off a bar of 'the new steel than a corresponding bar of ordinary 31/2% Ni steel when heated to about 1800 F. and handled under corresponding conditions. The free scaling property of the new steel also manifests itself during machining operations where it has been found that the surface layer or coating of a rod, for instance, can be removed much more easily than that on an ordinary nickel steel rod and that the edge of the cutting tool is not dulled as quickly` or as easily as it is when operating on g the ordinary nickel steels.

In Fig. 1, the photomicrograph indicates that there is a porous layer L interposed between the base metal B and the scale S. The porous layer L has a friable constitution and forms a weak bond between the outer coating of scale and the core or base metal. Ordinary steels do not show a structure of this sort.

Referring now to Fig. 2, the coating of scale C is bonded to the core K by means of dark solid material, apparently oxide, which tenaciously holds the coating of scale to the core of base metal. In the ordinary or untreated steels, it will be observed that a porous layer in the scale is wholly absent. f

As yet, no explanation has been found for the difference in structure between the scale of ordinary steel and the scale of the new steel. Tests, however, demonstate that there are fundamental differences between the scale on ordinary steel and the scale on the new steel. Among these differences the following may be noted:

1. Scale on ordinary steels is relatively tough and is tenaciously adherent to the foundation metal whereas scale on the new alloy steel is m5 friable and is loosely adherent.

2. The old scale generally has a reddish brown or rust color whilethe new scale has a grayish black color.

3. The structure of the old scale tends toward un a ldense type whereas that of the new scale is more or less porous.

4. The amount of scale formed and detached from a piece of old steel is substantially smaller than that from a piece of new steel when heated and handled under corresponding conditions.

5. Scale on the new steel is moreA easily removed by pickling, sand blasting, etc., than scale on ordinary steel.

The new steel has also been found to have improved machining qualities. For instance, the ordinary tendency of steel to tear was reduced, the smoothness of the cut surfaces was improved, the power required in machining operations was decreased by a substantial amount, and the life of the tools was increased substantially.

The grindings produced in machining of the new steel have a distinctly different appearance than the grindings of a corresponding untreated steel. Photomicrographs of grindings of the new 13? steel indicate and show a fibrous appearance or nature whereas the grindings of an ordinary steel appear to have a powdery nature.

Example No. 2

l.' The invention may also be carried into practice with higher carbon nickel steels. For example, a :l1/2% nickel steel having the following composition may be used:

Carbon 0. 43% 143 Nickel 3. 38% Manganese 0.65% Iron plus usual impurities Balance When a steel having this composition is treated with 0.40% of a sulphide of zirconium, it has improved properties over an untreated steel of similar composition as shownby the following table. The specimens were oil quenched from 1460 F.

and were oil tempered at 425 F. 150` meente? figures given in the illustrative examples.

Table Treated steel Untreated Properties (0.43 Q 4 3.38 N1) 3.38 Ni) Brinell hardness 512 512 Rockwell hardness C scale 50.5 50.5 Charpy impact energy absorbed 6ft. lbs 4.5 it. lbs. Izod impact energy absorbed 9.8 ft. lbs 10.5 It. lbs.

Treatid Untreaxted stee stee Step gears (0.43 C (0.50C 3.38 Ni) 3.38Ni) Scaling losses High Moderate. Freedom of scaling Very good- Poor Annealed steels Rough turning-surface nish Rough Rough Finish turning-surface finish Good Fair Example No. 3

A 5% nickel steel may also be used. For instance, a steel having the following composition:

Carbon 0. 17% Nickel 4. 56 Manganese 0. 35 llron plus customary impurities Balance By treating the foregoing steel with about 0.4% of a sulphide of zirconium, a steel is produced which has the following properties as compared to an ordinary untreated steel of similar composition. The specimens were carburized for 13 hours at 1'700u F. and then reheated and oil quenched from 1475 F.

Table A steel of the foregoing sort when embodying the present invention as by adding 0.5% of zirconium sulphide has the following improved properties and characteristics:

1. Easier and better machining resulting in faster cutting, better nish on the work pieces and less rapid tool wear.

2. Freer scaling resulting in cleaner surface and less scale to be removed by vthe cutting tool and better machining and cold forming properties.

In the foregoing examples reference has been made to certain specic compositions for the purpose of illustrating the invention but it is to be observed that the invention is not limited thereto but may be embodied in other compositions. For example, low alloy steels containing nickel and chromium, or manganese and molybdenum, o chromium and vanadium or any other of the low alloy steels well known to those skilled in the art.

In the same manner the percentages of the alloying metals or of the sulphides of zirconium or molybdenum may be varied from. the specific For instance, the sulphide of a given metal or a mixture of sulphides may be employed within a relatively wide range. In practice, it has been found better to express the amount of sulphide to be used in terms of equivalent sulphur con-v tent. It has been found that the sulphide or sulphides may be used in amounts equivalent g5 to a total sulphur content of from about 0.05% to 0.15% sulphur contained in the sul@l phides. Of course, the amount of sulphide or sulphides to be used in any given instance to produce the free scaling and free machining low an) alloy steels will depend upon the steels, the sulphides employed, the magnitude of the effects desired and the purposes for which the steels are intended. If the total sulphide content is too low the benefits derived will not be as good as g5 when higher amounts are used, while if the total sulphide content is too high the mechanical yproperties of the steels may be adversely affected.

It will be observed that sulphides other than zirconium or molybdenum which produce the results of the present invention may be employed.

It will be noted that the present invention provides a new alloy steel oi' corrosive type which not only has a relatively high strength and high degree of toughness and other required mechanical properties, but also possesses the property of being free scaling and free machining.

It is to be understood that when the term commercial iron is used in the specification or claims, it is intended to mean iron or steel con-A 11G taining sulfur, phosphorus, manganese, silicon, alloys including iron-carbon alloys, etc.

What is claimed is:

l. A nickel alloy steel containing about 1% to about 7% nickel and the balance comprising M5 substantially all commercial iron and having zirconium sulphide incorporated therein in such amount that the sulphur content thereof lies within a range from about 0.05% to about 0.15%, whereby a free scaling steel is produced which has easily detachable scale with a -riable intermediate layer, which forms a greater amount of scale when, heated and which requires a substantially lesser amount of power to machine than an untreated low nickel alloy steel.

2. A nickel alloy steel containing about 1% to about 7% nickel and the balance comprising substantially all commercial iron and having zirconium sulphide incorporated therein in such amount that the sulphur content thereof lies within a range from about 0.05% to about 0.15%, whereby a free scaling steel is produced which has easily detachable scale with a friable intermediate layer, which forms-a greater amount of scale when heated and which requires a substantially lesser amount o'f power to machine than an untreated low nickel alloy steel.

3. A nickel alloy steel containing about 1% to about 7% nickel and the balance comprising substantially all commercial iron and having zirconium sulphide ,incorporated therein in such amount that the sulphur content thereof lies within a range from about 0.05% to about 0.15%, whereby a free scaling steel is produced which has easily detachable scale with a friable intermediate layer, which forms a greater amount of scale when heated and which requires a substantially lesser amount of power to machine than an untreated low nickel alloy steel.

4. A nickel alloy steel containing about 1% to 150 scale when heated and which requires a substantially lesser amount of power to machine than an untreated low nickel alloy steel.

HERBERT JAMES FRENCH. JOHN WOODBURY SANDS. 

